Catheter for neural blockades

ABSTRACT

The invention relates to a catheter ( 10 ) for neural blockades in anaesthesia. Said catheter consists of a flexible plastic tube in which a wire ( 16 ) is arranged for electrostimulation. The distal end of said wire ( 16 ) is conductively applied to a contact tip protruding out of the catheter ( 10 ). Said contact tip consists of a stopper ( 12 ) and a cap ( 14 ) which are positioned in the catheter ( 10 ), the cap being arranged in front of the distal end of said catheter ( 10 ) and covering the edge of the front surface thereof.

BACKGROUND OF THE INVENTION

The present invention relates to the field of catheters, and inparticular to a catheter for nerve blocks in anesthesia.

In anesthesia, for lengthy operations, postoperative pain therapy, andtreatment of chronic pain states, the nerves supplying a specific regionof the body are often blocked by an anesthetic. A catheter is used tointroduce the anesthetic, and the distal end of the catheter ispositioned as close as possible to the nerve to achieve an optimumeffect with a minimal quantity of anesthetic. The catheter, which canremain in position for a long time if necessary, includes a long, thin,flexible plastic tube.

To insert the catheter into the sheath or canal of the nerve, a cannulais used to insert the catheter. U.S. Pat. No. 5,007,902 teachesreplacement of such a cannula by a puncture cannula, in which case thepuncture cannula is pulled away in order to insert the catheter. Germanpatent DE 3643235 C1 teaches a puncture cannula whose internal canalemerges at the side behind the distal tip of the cannula, with thecatheter being inserted and positioned by means of this puncturecannula. Once the catheter is in position, the cannula used for itsinsertion is removed.

U.S. Pat. No. 5,007,902 also teaches the use of electrical nervestimulation for precise positioning of the catheter. In this case, aguide wire is inserted in the catheter, and its distal end protrudesslightly from the distal end of the catheter. The proximal end of theguide wire is electrically contactable for connection of a stimulator.Using electrical simulation, the position of the distal end of thecatheter can be determined exactly while the catheter is being insertedinto the sheath or canal of the nerve. Since the guide wire completelyfills the internal cross section of the catheter, the wire has to beremoved from the catheter as soon as the catheter is in place in orderto apply the anesthetic through the catheter. If the catheter remains inplace for a long period of time and further medication has to beintroduced, it is often necessary to check the position of the catheterand possibly correct it. It is necessary for this purpose to insert aguide wire once again to determine the position of the distal end of thecatheter by electrical stimulation.

It is also known that a thin wire can be disposed in the catheter forelectrical stimulation, the cross section of which is smaller than thefree internal cross section of the catheter. In this way, the wire doesnot impede introduction of a liquid through the catheter so that thewire can remain in the catheter. The position of the wire, fixedlydisposed in the catheter, can be checked by electrical stimulation andcorrected for the entire time that it is in place. However, if the thinend of the wire protrudes from the distal end of the catheter, there isa risk that the tip of the wire may cause damage and injury to thenerves while the catheter is being pushed forward. If the wire does notprotrude from the distal end of the catheter, although this risk isreduced the electrical contact for electrical stimulation is no longerreliably assured.

Therefore, there is a need for a catheter for a nerve block that can bepositioned by electrical stimulation, ensuring a reliable contact forelectrical stimulation and a minimal risk of injury, and making itpossible for the catheter position to be checked at any time byelectrical stimulation.

SUMMARY OF THE INVENTION

A contact tip is placed in the distal end of the catheter, comprising ametal part inserted coaxially with a plug into the distal end of thecatheter, protruding with a cap at the distal end of the catheter, andoverlapping the edge surface thereof. For an electrically conductiveconnection between this contact tip and the proximal end, a thin wire isdisposed in the catheter which is connected in an electricallyconducting fashion with the plug of the contact tip. The contact tipwith its cap forms the distal end of the catheter. The cap provides areliable electrical contact over a large surface area for nervestimulation. The blunt, rounded cap overlapping the distal end of thecatheter also avoids the risk of injuring the nerve as the catheterslides forward. The plug inserted into the distal end of the catheterkeeps the contact tip centered in the distal end of the catheter. Thethin wire passing through the catheter in order to connect the distalcontact tip with the proximal connector of the stimulator does notprevent a liquid such as an anesthetic from being introduced. Electricalstimulation is possible as the catheter is being inserted for exactpositioning and can be repeated at any time while the catheter is inplace to check, and if necessary correct, its position.

The contact tip can completely close off the distal end of the catheter.In this case, the liquid introduced through the catheter exits distallythrough outlet openings provided in the catheter wall at its distal endarea immediately behind the contact tip. In another embodiment, thecontact tip can have an axial hole through which the liquid can pass. Inthis case, outlet openings in the catheter wall are not necessary, butcan be provided in order to enlarge the outlet cross section. The outletopenings in the catheter wall are preferably formed so that, with theircenter axis, that is the outlet direction, they form an acute angle ofless than 90° with the center axis of the catheter, with this acuteangle opening in the distal direction. The acute angle can beapproximately 45° in one preferred embodiment. The shape of the outletopenings at an angle in the forward direction causes the liquidintroduced through the catheter to exit in the distal direction so thatthe liquid, for example an anesthetic, is precisely applied.

These and other objects, features and advantages of the presentinvention will become more apparent in light of the following detaileddescription of preferred embodiments thereof, as illustrated in theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an axial section through the distal end of the catheter in afirst embodiment;

FIG. 2 is a corresponding view of a second embodiment;

FIG. 3 is a corresponding view of a third embodiment;

FIG. 4 is a corresponding view of a fourth embodiment;

FIG. 5 is a corresponding view of a fifth embodiment; and

FIG. 6 is a lateral view of the distal end of the catheter without thecontact tip, in partial axial section.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a cross section view of a catheter 10. The catheter 10 is aflexible tube, made for example of plastic or polyamide. The length ofthe catheter 10 depends on its application. For peripheral plexusanesthesia, the length of the catheter 10 is approximately 400 mm, whilefor peridural and spinal anesthesia a length of for example 900 mm maybe used. The diameter of the catheter 10 also depends on theapplication. For example, a 19 G catheter has an external diameter of 1mm and an internal diameter of 0.5 mm. A 20 G catheter has an externaldiameter of 0.8 mm and an internal diameter of 0.4 mm. It is possible touse a still thinner catheter with correspondingly smaller diameters.

The catheter 10 includes a contact tip that is placed in the distal endof the catheter 10, and is formed as a metal part. The contact tipincludes a plug 12 and a cap 14, in one piece. The plug 12 has the shapeof a circular cylinder whose external diameter corresponds to theinternal diameter of the catheter 10. This makes it possible to insertthe plug 12 of the contact tip into the distal end of the catheter 10 sothat the plug 12 is held with a snug fit in the catheter 10. Theexternal diameter of the cap 14 corresponds to the external diameter ofthe catheter 10. When the contact tip is inserted into the distal end ofthe catheter 10, the plug 12 is pushed into the lumen of the catheter 10until the cap 14 abuts the distal end surface of the catheter 10. Sincethe diameter of the plug 12 corresponds to the internal diameter of thecatheter 10, the plug 12 holds the contact tip in the center at thedistal end of the catheter 10 with the cap 14 overlapping and coveringthe edge surface of the catheter 10. At the outer periphery, the cap 14fits flush to the catheter 10 so that the cap 14 fits seamlessly intothe outer periphery of the catheter 10.

For an electrically conductive connection of the contact tip with astimulator (not shown) connected at the proximal end of the catheter, athin wire 16 is disposed in the catheter 10. The diameter of the wire 16is considerably smaller than the internal diameter of the catheter 10,so that a considerable portion of the lumen of the catheter 10 remainsfree for a liquid to pass through. The diameter of the wire 16 is forexample 0.2 mm. The proximal end of the wire 16 is contactable with thestimulator in a manner not shown. The distal end of the wire 16 isconnected in an electrically conducting fashion with the plug 12 of thecontact tip, for example soldered, glued, embossed, or laser-welded. Anumber of embodiments of the contact tip are described below.

In the embodiment of FIG. 1, the plug 12 and the cap 14 are closed. Thecap 14 is in the shape of a hemisphere whose curved portion is on thedistal side. The wire 16 is soldered coaxially into a blind holeprovided coaxially in the inside end surface of the plug 12.

In the embodiment of FIG. 2, the cap 14 is also in the shape of ahemisphere. A through-hole 18 passes through the contact tip (i.e.,through the plug 12 and the cap 14), and runs eccentrically and axiallyparallel thereto. The blind hole that receives the wire 16 is locatedaxially parallel and externally diametral to the through-hole 18.

In the embodiment of FIG. 3, the cap 14 is also hemispherical. Thethrough-hole 18 passes coaxially through the plug 12 and the cap 14. Thewire 16 is soldered into a groove formed axially in the outer peripheryof the plug 12.

In the embodiment of FIG. 4, the cap 14 is in the shape of a flat platethat extends from a smooth distal end surface starting at the outercircumference with a radius of curvature and makes a transition to thecylindrical circumferential surface of the catheter 10. As in theembodiment of FIG. 3, the through-hole 18 is coaxial and the wire 16 isset in an axial circumferential groove.

In the embodiment of FIG. 5, the cap 14 is in the shape of a hemisphere.The through-hole 18 is coaxial, and has a larger diameter toward theinside end of the plug 12. A hollow bushing 20 is inserted into thisenlarged section of through-hole 18, and includes an inside wall towhich the wire is electrically connected.

If the contact tip has an axial through-hole 18, a liquid such as ananesthetic can be added through the catheter 10 and exit through thisthrough-hole 18. If the contact tip is closed, as for example in theembodiment of FIG. 1, one or more outlet openings 22 are provided in thedistal end area of the catheter 10 behind the contact tip, through whichopenings the liquid can exit. Such outlet openings 22 can also beprovided in cases where the contact tip has an axial through-hole 18 toenlarge the cross section for the added liquid to exit.

The outlet openings 22 may have any shape, cross section, andarrangement. A design such as that shown in FIG. 6 is preferable. Inthis design, the outlet openings 22 are provided in the wall of thecatheter 10 such that the center axis of the outlet opening 22 makes anacute angle with the center axis of the catheter 10 (e.g., an angle of45°), with this acute angle opening in the distal direction. In thisway, the liquid added is directed distally through the outlet openings22. Three outlet openings 22 are provided, making angles of 120° witheach other in the circumferential direction. This ensures that theliquid added is dispensed evenly over the entire periphery of the distalend of the catheter 10. In order for the outlet openings 22 not toweaken the wall of the catheter 10, the outlet openings 22 arepreferably offset axially from each other.

Although the present invention has been shown and described with respectto several preferred embodiments thereof, various changes, omissions andadditions to the form and detail thereof, may be made therein, withoutdeparting from the spirit and scope of the invention.

1. A catheter for a nerve block in anesthesia comprising: a flexibleplastic tube that forms a lumen and includes a tube proximal end and atube distal end; a wire in said catheter for electrical stimulation,whose wire proximal end is electrically contactable at the tube proximalend and which leads to a contact tip protruding distally from saidcatheter, where the contact tip is a metal part that includes a plug anda cap, wherein said plug is insertable coaxially into the distal end ofsaid catheter, that said cap is disposed in front of said tube distalend and overlaps its distal edge surface, that the cross section of saidwire is smaller than the free internal cross section of said catheter,and said wire is connected in an electrically conducting fashion at itswire distal end with said plug, wherein the wall of said catheter has atleast one outlet opening at its distal end area behind said plug and thecenter axis of the at least one liquid outlet opening makes an acuteangle of less than 90° with respect to the center axis of said catheterin the distal direction, whereby fluid injected into the proximal end ofthe tube is directed generally in the distal direction.
 2. The catheterof claim 1, wherein said plug and said cap form a single metal part. 3.The catheter of claim 2, wherein said wire is soldered, glued, embossed,or laser-welded to said plug.
 4. The catheter of claim 3, wherein saidcap is blunt and rounded, and makes a smooth transition at its outerperiphery into the outer contour of said catheter.
 5. The catheter ofclaim 4, wherein said cap is in the shape of a hemisphere.
 6. Thecatheter of claim 4, wherein through-hole passes axially through saidplug and said cap.
 7. The catheter of claim 1, wherein said at least oneoutlet opening comprises three outlet openings offset by 120° in thecircumferential angle, and offset axially to each other.
 8. The catheterclaim 1, wherein said at least one outlet opening comprises three outletopenings offset by 120° in the circumferential direction, and offsetaxially to each other.